The invention relates to a lighting system, in particular for motor vehicles, and to a method of generating a light beam of desired shape.
Lighting systems and associated methods of generating light beams have been known for a long time in a wide variety of shapes. It is common to all relevant lighting systems and methods that light is generated by means of a light source, which light is then shaped into a beam by various optical means, such that the light beam of desired shape is obtained. Light sources particularly widely used in the field of motor vehicles are halogen incandescent lamps, and in recent years increasingly gas discharge lamps, more in particular low-voltage gas discharge lamps such as, for example, so-called MPX lamps (Micro Power Xenon lights). The discharge lamps do indeed have major advantages over incandescent lamps as regards their useful life and power dissipation, but the light arc generated thereby has no exact demarcation, in contrast to a coil of an incandescent lamp, and is accordingly optically and photometrically more difficult to control.
To form the desired light beam from the light generated by the light source, first of all parabolic reflectors are known, which project the light source directly onto the surface to be illuminated, i.e. onto the road surface in the case of motor vehicles. The final beam composition is achieved by means of a divergent lens, usually a combination of prismatic and cylindrical lens arrays, which closes off the lighting system at the front. In addition, projection systems are known in which an elliptical reflector pictures the light source at a distance of a few centimeters in front of the lamp. A metal plate is present adjacent this plane in motor vehicle headlights as a mechanical cut-off diaphragm of special shape so as to generate a light-dark edge necessary for a passing beam. A projection lens images this cut-off and the light source on the road surface. Very high-contrast light-dark edges can be generated by this principle of beam generation, but they do show a clear color edging effect.
An improvement of the beam properties is achieved through the use of so-called complex-shape or profiled reflectors. The geometry of the reflector is calculated in small segments with a view to their effect on the headlight beam. A reflector geometry is created thereby which differs from classical rotational (elliptical or parabolic) surfaces. It is possible with complex-shape reflectors in headlights containing halogen incandescent lamps to achieve a sufficiently high contrast at the light-dark edge without a screen cap. A dispersing front lens for influencing the beam can be dispensed with thanks to the improved reflector geometry in the case of such reflectors. A clear cover disc suffices in this case.
High requirements are imposed on the positioning of the light source in the reflector in the known lighting systems with wide-aperture reflectors, which collect the light from the light source and thus build up the headlight beam. This is particularly apparent with the use of gas discharge lamps as the light source, because the light arc does not have sharp boundaries, in contrast to the coil of incandescent lamps.
Increasingly stringent requirements imposed on the beam quality also imply increasingly stringent requirements on the positioning of the light source in the reflector. Since this light source should as a rule be supported so as to be exchangeable, the exact positioning poses a problem. On the one hand, the lamps should be capable of exchange in a simple and fast manner, while on the other hand they must be securely and accurately fastened, and it must be possible to manufacture the fastening devices in use at an affordable cost. This has the result that manufacturing tolerances of the fastening devices used limit the effectivity and the light power of the entire system.
In view of the above, it is an object of the invention to provide a lighting system, in particular for motor vehicles, and a method of generating a light beam of desired shape wherein the exact positioning of the light source relative to the other optical components only has a minor influence on the light output and the efficiency of the entire system, and on the generation of the desired light beam.
This object is achieved by means of a lighting system, in particular for motor vehicles, which comprises at least one light source, preferably in the form of a high-power discharge lamp (HID lamp: High Intensity Discharge lamp), in particular a low-voltage xenon lamp (MPXL: Micro Power Xenon Light), a collector which surrounds the light source at least partly for collecting and passing on the light generated by the light source to at least one separator, and at least one separator of optical waveguide material, while each separator comprises at least one specially shaped light outlet surface for radiating the light, which was guided into the separator, as a light beam of defined shape.
The arrangement according to the invention has a considerable number of advantages. Thus it is made possible to generate the clearly defined light-dark edge required, for example, for the passing beam in the field of motor vehicles through a suitable construction of the collector without absorption and to image this edge by means of one or preferably several separators. Until now, by contrast, the edge was generated by means of cut-off diaphragms, which block out part of the generated light and thus reduce the efficiency of relevant lighting systems unnecessarily. In a lighting system according to the invention, however, practically the entire quantity of light generated by the light source(s) can be utilized for illumination, so that a very high efficiency is achieved.
A further major advantage of the arrangement according to the invention is that very compact lighting systems can be realized thereby, whose constructional dimensions are strongly reduced in comparison with conventional systems.
In a particularly preferred embodiment, the light source, the collector, and the separator(s) are arranged such that a so-called interwoven radiation path is obtained. For this purpose, the separator(s) and the collector are arranged relative to one another such that part of the image of the light source generated by the collector lies within the range of the entrance pupil of each separator. A separation of the lighting beam path (of the image of the light source) and imaging beam path (of the image of the object to be imaged, i.e. the collector in this case) is advantageously achieved in this manner, so that the light outlet surface(s) thereof can generate sharp light-dark edges.
If the light-dark edge lies adjacent or in a pupil of the lighting beam path, an inaccurate alignment of the light source will not or substantially not affect the contrast of the light-dark edge. According to the invention, the collector, with sharp edges regarded as the object lying in its emission surface, takes over the function of the known condenser lenses or the optical lighting system.
In particular, the size of the light source in this arrangement has practically no influence on the aperture in the headlight beam, but only on the diameter of the separators. By contrast, the light source is directly imaged onto the road surface in headlights for motor vehicles presently on the market, i.e. each segment of the reflector generates a sharp picture of the incandescent coil or the light arc on the road surface.
If the diameter of the separators is greater than or at least equal to the size of the virtual light source image, the radiation beam is not cut off, and the efficiency of the lighting system will be very high.
The dissociation of the shape of the radiated light beam from the size and alignment of the incandescent coil renders it possible to keep the aperture of the light beams originating from the light source small without the usual photometric problems, a small aperture being desired as a rule because the constructional dimensions of the collector are directly dependent on this aperture if the collector is to operate with a very high efficiency. Light sources with an aperture of less than 60xc2x0, preferably between 20xc2x0 and 40xc2x0 and even lower, may be used.
The interwoven beam path furthermore leads to an increase in the efficiency also with the use of conventional discharge lamps, because light can now also be utilized which is scattered in the so-called salt reservoir formed during operation of such discharge lamps. The interwoven beam path means that the arc need no longer be sharply pictured into the headlight beam, so that a stronger scattering of the light only has a minor influence on the beam.
If a discharge lamp with a lamp bulb is to be used as the light source, discharge lamps with a cylindrical or sagged bulb shape were found to be particularly suitable.
The collector is preferably constructed as a solid component and is formed by a transparent, heat-resistant material, preferably glass. Depending on which light source is used, the collector may alternatively be formed from a synthetic resin with optical waveguide properties, which may have advantages as regards weight compared with glass. The great heat arising with the use of conventional gas discharge lamps, however, implies that only few synthetic resins are suitable as collector materials.
The collector preferably has an annular light outlet surface, so that advantageously many applications can be served with one and the same xe2x80x9cstandardizedxe2x80x9d collector shape through the use of different separators.
Depending on the shape of the desired light beam and the application, it may suffice to arrange only one separator behind the collector. It was found to be particularly suitable, however, especially for generating the light beam desired for the passing beam in the field of motor vehicles, to distribute the light from the collector over several, preferably six to ten separators, and then to superimpose the light beams radiated by the separators so as to form the light beam of desired shape.
If scattering of the light issuing from the separator(s) is desired, the light outlet surfaces of the separators may for this purpose have a structure similar to that of a dispersing lens. This has the advantage that a separate dispersing lens, and accordingly a further material-air-material transition of the light, which is always accompanied by light losses, can be omitted.